420 research outputs found
Quality assurance procedures for V378A matrix resin
A characterization methodology has been developed on which to base quality assurance procedures for U.S. Polymeric V378A bismaleimide matrix resin. Chemical composition is established by partition reverse phase and size exclusion liquid chromatography. Cure rheology behavior is quantitatively characterized by dynamic viscoelastic analysis using the parallel plate technique. The overall cure process is characterized by differential scanning calorimetry. The sensitivity of the procedures is evaluated by studying the effects of ambient out time on the chemical end behaviorial properties of the resin
Development and demonstration of manufacturing processes for fabricating graphite/LARC 160 polyimide structural elements
The development and demonstration of manufacturing technologies for the structural application of Celion graphite/LARC-160 polyimide composite material is discussed. Process development and fabrication of demonstration components are discussed. Process development included establishing quality assurance of the basic composite material and processing, nondestructive inspection of fabricated components, developing processes for specific structural forms, and qualification of processes through mechanical testing. Demonstration components were fabricated. The demonstration components consisted of flat laminates, skin/stringer panels, honeycomb panels, chopped fiber compression moldings, and a technology demonstrator segment (TDS) representative of the space shuttle aft body flap
Crossover from phase fluctuation to amplitude-dominated superconductivity: A model system
We have experimentally studied a model system that demonstrates the crossover from a superconductor that is dominated by phase fluctuations, to one in which the amplitude of the order parameter is the controlling influence on Tc. This model system is comprised of two-dimensional granular Pb with an overlayer of Ag. The system displays many aspects of the phase diagram of the concentration dependence of Tc in the high-Tc superconductors, and this crossover has been applied to explain the phase diagram in that case. We point out the similarities and differences between the model system presented in this paper and the high-Tc superconductors
Exploring the anthelmintic properties of Australian native shrubs with respect to their potential role in livestock grazing systems
We measured in vitro anthelmintic activity in extracts from 85 species of Australian native shrub, with a view to identifying species able to provide a degree of worm control in grazing systems. Approximately 40% of the species showed significant activity in inhibiting development of Haemonchus contortus larvae. The most active extracts showed IC50 values of 60–300 mg/ml. Pre-incubation with polyvinylpolypyrrolidine removed the activity from some extracts, implicating tannins as the bioactive agent, while in other cases the pre-incubation had no effect, indicating the presence of other anthelmintic compounds. Plant reproductive maturity (onset of flowering or fruiting) was associated with increasing anthelmintic activity in some species. Variability was observed between plants of the same species growing in different environments, while variation between individual plants of the same species within a single field suggests the existence of distinct chemotypes. Significant activity against adult H. contortus worms in vitro was also demonstrated in a limited number of extracts tested against this life stage. Our study indicates that there is potential for Australian native shrubs to play an anthelmintic role in grazing systems, and highlights some plant biology factors which will need to be considered in order to maximize any anthelmintic effects.A. C. Kotze, J. O’Grady, J. Emms, A. F. Toovey, S. Hughes, P. Jessop, M. Bennell P. E. Vercoe and D. K. Revel
A High Speed, Post-Processing Free, Quantum Random Number Generator
A quantum random number generator (QRNG) based on gated single photon
detection of an InGaAs photodiode at GHz frequency is demonstrated. Owing to
the extremely long coherence time of each photon, each photons' wavefuntion
extends over many gating cycles of the photodiode. The collapse of the photon
wavefunction on random gating cycles as well as photon random arrival time
detection events are used to generate sequences of random bits at a rate of
4.01 megabits/s. Importantly, the random outputs are intrinsically bias-free
and require no post-processing procedure to pass random number statistical
tests, making this QRNG an extremely simple device
Direct measurement of quasiparticle-lifetime broadening in a strong-coupled superconductor
We have measured the quasiparticle recombination time in the strong-coupled superconductor Pb0.9Bi0.1 directly by measuring the lifetime-broadened energy gap edge. This is done by measuring the I-V characteristics of a superconducting tunnel junction of the type Pb0.9Bi0.1-insulator-Pb0.9Bi0.1. Agreement with the calculated value is excellent
Josephson scanning tunneling microscopy: A local and direct probe of the superconducting order parameter
Direct measurements of the superconducting superfluid on the surface of
vacuum-cleaved Bi2Sr2CaCu2O8(BSCCO) samples are reported. These measurements
are accomplished via Josephson tunneling into the sample using a scanning
tunneling microscope (STM) equipped with a superconducting tip. The spatial
resolution of the STM of lateral distances less than the superconducting
coherence length allows it to reveal local inhomogeneities in the pair
wavefunction of the BSCCO. Instrument performance is demonstrated first with
Josephson measurements of Pb films followed by the layered superconductor
NbSe2. The relevant measurement parameter, the Josephson ICRN product, is
discussed within the context of both BCS superconductors and the high
transition temperature superconductors. The local relationship between the ICRN
product and the quasiparticle density of states (DOS) gap are presented within
the context of phase diagrams for BSCCO. Excessive current densities can be
produced with these measurements and have been found to alter the local DOS in
the BSCCO. Systematic studies of this effect were performed to determine the
practical measurement limits for these experiments. Alternative methods for
preparation of the BSCCO surface are also discussed.Comment: 53 pages, 26 figures, editorially accepted for Physical Review
Calorimetric readout of a superconducting proximity-effect thermometer
A proximity-effect thermometer measures the temperature dependent critical
supercurrent in a long superconductor - normal metal - superconductor (SNS)
Josephson junction. Typically, the transition from the superconducting to the
normal state is detected by monitoring the appearance of a voltage across the
junction. We describe a new approach to detect the transition based on the
temperature increase in the resistive state due to Joule heating. Our method
increases the sensitivity and is especially applicable for temperatures below
about 300 mK.Comment: 10 pages, 5 figures. To appear in the proceedings of the Conference
on Micro- and Nanocryogenics (LT25 satellite) organized in Espoo, Finland
(2008
Scanning Tunneling Spectroscopy in MgB2
We present scanning tunneling microscopy measurements of the surface of
superconducting MgB2 with a critical temperature of 39K. In zero magnetic field
the conductance spectra can be analyzed in terms of the standard BCS theory
with a smearing parameter Gamma. The value of the superconducting gap is 5.2
meV at 4.2 K, with no experimentally significant variation across the surface
of the sample. The temperature dependence of the gap follows the BCS form,
fully consistent with phonon-mediated superconductivity in this novel
superconductor. The application of a magnetic field induces strong
pair-breaking as seen in the conductance spectra in fields up to 6 T.Comment: 4 pages, 4 figure
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